This application claims the priority of German application 197 56 016.4, filed in Germany on Dec. 17, 1997, the disclosure of which is expressly incorporated by reference herein.
The invention relates to a device for hydraulic rotational angle adjustment of a shaft relative to a drive wheel, especially the camshaft of an internal combustion engine. Preferred embodiments of the invention relate to such a device having an inner part connected nonrotatably with the camshaft, said inner part having at least approximately radial ribs or vanes, and a driven compartmented wheel that has a plurality of compartments distributed around the circumference, which are subdivided by ribs or vanes into two pressure chambers, which, when pressurized, rotate the camshaft relative to the compartmented wheel by pressure acting on the ribs or vanes.
A device of this kind is known for example from U.S. Pat. No. 4,858,572. In this device, an inner part is connected nonrotatably with the end of the camshaft, which has on its exterior a plurality of radial slots distributed around the circumference, in which slots vane elements are guided radially displaceably. This inner part is surrounded by a compartmented wheel which comprises a plurality of hydraulically pressurizable compartments that are divided by the vanes into two pressure chambers that act against one another on the compartments. By pressurization of these pressure chambers, depending on the pressure differential, the compartmented wheel can be rotated relative to the inner part and hence to the camshaft. In addition, in the compartmented wheel, a hydraulically pressurizable piston is guided in each of two radial bores in defined angular positions, said pistons being capable of being pushed into a radial depression of the inner part in the associated end position of the device. These pistons are urged by compression spring elements in the direction of the inner part and are displaceable in the opposite direction by hydraulic pressurization of the bores in the inner ring. The device is intended to be locked in one of its two end positions by these spring-loaded pistons, provided the pressure for pressurizing the pressure chambers has not yet reached a certain level. It is only when a certain pressure level is reached that the pistons are pushed back against the action of the compression springs and allow the inner part to rotate relative to the compartmented wheel. With such a device, it is intended among other things to eliminate rattling noises when starting the internal combustion engine, said noises being produced by alternating changes in torque when starting and operating the internal combustion engine.
In addition, a device for hydraulic rotational angle adjustment of a camshaft relative to its drive wheel is known from German Patent Document DE 39 37 644 A1, in which a plurality of radially-extending ribs is permanently connected to an inner part that is nonrotatably connectable with the camshaft, said ribs being rotationally movable in the compartments of a surrounding compartmented wheel and dividing these compartments into two pressure chambers each. Means for securing the rotational position of the shaft relative to the compartmented wheel are not provided in this case, however.
Devices of this kind for relative rotational angle changing of a camshaft relative to a drive wheel have the disadvantage that the rotational angle change, because of the alternating effect with the torque fluctuations that are caused by the valve drive during the constant rotation of the camshaft is not uniform but shows constant position deviations during the adjustment process. Devices of this kind have a more-or-less markedly nonuniform pattern of changes in rotational angle.
On the other hand, a goal of the invention is to improve a device of the above described general type for relative rotational angle changing of a camshaft of an internal combustion engine relative to a drive wheel in such fashion that the adjustment process is made uniform and the influence of alternating torques from the drive of the camshaft during the adjustment process is minimized.
This goal is achieved according to preferred embodiments of the invention, by integrating damping structure into the device to hydraulically damp the rotational angle changes of the device. By means of a hydraulically acting damping in the manner of a throttle or a diaphragm, overlapping of the rotational movement caused by the alternating torques that develop can be damped to a greater extent than the desired change in rotational angle by the pressurization of the pressure chambers. The integration of the damping structure directly into the device formed essentially by the inner part and the compartmented wheel also has the advantage that long line lengths between the damping means and the effective pressure chambers, which in turn would negatively influence the damping properties and would also involve additional structural expense, are avoided.
These hydraulically acting damping structures can be designed advantageously as damping throttles between two hydraulically pressurized pressure chambers.
The damping effect is especially good if both of the pressure chambers connected by the damping throttles are constantly pressurized with system pressure, with the volume of one pressure chamber during a change in rotational angle relative to another being reduced or increased, and the enclosed pressure medium then being forced by the damping throttle out of one pressure chamber and into the other.
The damping throttle can be designed in an especially advantageous manner that is favorable from the manufacturing standpoint as a leakage channel of a certain size between the two pressure chambers.
The manufacture of such a device and the design of a damping throttle are especially simple and inexpensive from the manufacturing technology standpoint if the two pressure chambers are adjacent to one another and the damping throttle is formed by a gap of a specified size between a rib or a vane and the adjacent opposite surface of the inner part or compartmented wheel.
The foregoing disclosure has been set forth merely to illustrate the invention and is not intended to be limiting. Since modifications of the disclosed embodiments incorporating the spirit and substance of the invention may occur to persons skilled in the art, the invention should be construed to include everything within the scope of the appended claims and equivalents thereof.